A vehicle may include an engine that may be automatically stopped and started to conserve fuel. The engine may be stopped via a controller in response to vehicle operating conditions without receiving a specific request to stop the engine from a human driver or occupant of the vehicle. However, before the controller automatically stops the engine, specific vehicle operating conditions may have to be present. For example, a battery state of charge (SOC) may have to be greater than 70% and a battery temperature may have to be greater than 0° C. before the engine is permitted to automatically stop. The SOC and battery temperature thresholds are boundary conditions that are a basis for permitting or inhibiting automatic engine stopping and starting because a capacity of a lead-acid battery to crank an engine decreases at lower SOC and engine temperature. The battery SOC and temperature thresholds may also be useful to ensure desired engine starting performance during conditions of corrosion of electrical engine starting components and an aged starter. In addition, since the battery's capacity to crank an engine at a particular battery SOC and temperature decreases as the battery ages, battery SOC and temperature thresholds may be useful to ensure engine cranking performance is maintained at a desired level. On the other hand, if a battery is replaced, engine cranking performance may improve. However, because the SOC and battery temperature thresholds define minimum conditions for automatic engine stopping and starting, opportunities to automatically stop and start an engine may not be increased even though engine cranking performance may be increased due to the new battery.
The inventors herein have recognized the above-mentioned issues and have developed an engine operating method, comprising: decreasing a battery state of charge threshold in response to an automatic engine cranking time being less than a first threshold amount of time via a controller; and automatically stopping and starting an engine in response to a battery state of charge being greater than the battery state of charge threshold via the controller.
By decreasing a battery state of charge threshold in response to an automatic engine cranking time being less than a first threshold amount of time, it may be possible to provide the technical result of automatically stopping and starting an engine at lower battery SOC levels when a battery is new and has capacity to crank an engine at a speed that allows the engine to start quickly even though battery SOC is not at a very high level. Consequently, there may be more opportunities to stop the engine so that fuel may be conserved. As the battery ages, the SOC threshold may be increased so that vehicle occupants may not be concerned with longer cranking times that may be associated with starting an engine with an aged battery that has a low SOC.
The present description may provide several advantages. In particular, the approaches may improve vehicle drivability for some drivers. Further, the approaches allow automatic engine stopping and starting to be permitted more frequently during some conditions. Further still, the approach may provide more consistent engine cranking times over a life cycle of a battery.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.